Bug 1841 Partial Revert

Revert the apt proxy in stage 3 as it appears that the cache gets
crossed packages if 2 or more builds run at the same time.  Evidence
of problem is hash mismatch on osm_devops deb file during stage 3

Change-Id: Id8680453fd4588ca526ab1ea9cb8a322075e2386
Signed-off-by: beierlm <mark.beierl@canonical.com>